Docs: Document release tooling

[JReinhold]

Closes #22609

What I did

Added documentation for the release tooling and process. See this for a rendered version:
https://github.com/storybookjs/storybook/blob/release-docs/CONTRIBUTING/RELEASING.md

I just added it at CONTRIBUTING/RELEASING.md but I don't care much about where this documentation lives, inputs are welcome. I don't think it's appropriate in the contribute section on the docs site though

How to test

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[vanessayuenn]

This is so comprehensive! Good work 🔥🔥🔥

I have a couple of nits around the wording -- left suggestions for those. Regarding release cadence, I think we need to discuss it more thoroughly before writing anything down in a public document. I suggest leaving this topic out of the current document and instead discussing it as a team at the offsite next week. Once we have come to an agreement, we can commit to it in writing.

[jonniebigodes]

@JReinhold, this is amazing. Fantastic job on this. I left a couple of nits regarding phrasing for you to consider. Let me know and we'll go from here.

[JReinhold]

@jonniebigodes @vanessayuenn I've adressed all your comments now.